1. Field of the Invention
The invention relates to a magnetic-inductive flowmeter with at least one measuring tube, the measuring tube having at least one measuring section, with at least one magnetic field generating apparatus for generating a magnetic field in the measuring section of the measuring tube, and with at least two electrodes which are located in the measuring section of the measuring tube for detecting the measurement voltage, the magnetic field generating apparatus having at least one magnet coil which is located preferably outside the measuring section of the measuring tube with a coil core.
2. Description of Related Art
For flow rate measurement with a magnetic-inductive flowmeter a measuring tube is used which is preferably composed of a nonmagnetic material, for example, of plastic or a nonmagnetic metal which is electrically insulated from the measurement fluid in the region of the measuring section of the measurement medium or the measurement fluid, for example, a liquid, a gas or a mixture of a liquid and solids located in it. According to the prior art, in operation, a magnetic field which has been generated by a magnetic field generating apparatus permeates the measuring tube in the measuring section at least in part essentially perpendicular to the flow direction of the measurement medium. If the measurement medium has a minimum electrical conductivity, during flow of the medium its charge carriers are deflected by the magnetic field. On electrodes which are located perpendicular to the magnetic field and to the flow direction and which are coupled either conductively or capacitively to the measurement medium, charge separation causes an electrical potential difference which is detected with a measurement device and is evaluated as a measurement voltage. Since the measurement voltage which can be tapped is proportional to the flow velocity of the charge carriers which are moved with the measurement medium, the flow velocity can be deduced from the measurement voltage which can be tapped and the flow rate in the measuring tube can then be deduced from the flow velocity.
The magnetic field generating apparatus in the prior art generally is comprised of at least one magnet coil with a coil core and of two pole shoes which are facing one another and of which at least one is connected in a magnetically conductive manner to the magnet coil or the core of the magnet coil. Energizing the magnet coil or the magnet coils generally produces an alternating magnetic field in the measuring section of the measuring tube.
The level of the measurement voltage which can be tapped on the electrodes is especially dependent on the strength of the acting magnetic field. Therefore, in the prior art, measures are taken to increase the strength of the acting magnetic field, but also to enhance the homogeneity of the acting magnetic field.
The magnetic-inductive flowmeter on which the invention is based is known from a German patent application, specifically from German Patent Application DE 10 2006 060 442 A1. In this known magnetic-inductive flowmeter, the magnetic field generating apparatus is made in two parts; specifically, two modules which can be plugged into one another and which each have one magnet coil. The modules are attached to the outside wall of the measuring tube by clamping for purposes of measurement, and the measuring tube has a flattened shape in the measuring section which is encompassed by the modules. The entire magnetic field generating apparatus is therefore located outside the measuring tube in the known magnetic-inductive flowmeter on which the invention is based.
For the configuration of magnetic-inductive flowmeters generally two different conditions must be met or there is an effort to achieve the corresponding optimization. On the one hand, it is desired to achieve an increase of the measurement accuracy, for which reason the aforementioned procedure for increasing the magnetic field strength or also the optimization of the shape of the magnetic field within the measuring section are used. On the other hand, the outer dimensioning of the flowmeter is to be held to a minimum since flowmeters are used in process systems in which often a shortage of space prevails making it advantageous for the flowmeter itself to be as small or compact as possible.